The present invention relates to apparatus and techniques for aiding the design, quality control and manufacturing testing of light sources, being more particularly directed to light emitting diode (LED) light sources and the use of integrating spheres for measuring their output.
Manufacturers of various lamp-type light sources have long used optical integrating spheres for measuring the output characteristics of the lamps both during the design and quality control processes. In the design phase, integrating spheres are used to test new designs, and in the manufacturing phase, for SPC (statistical process control) testing and then life testing with periodic measurements of the lamp output characteristics of each lamp. Current integrating spheres are, for example, of the type described in U.S. Pat. No. 5,537,203 of Labsphere Inc., the common assignee of the present invention, marketed under the mark Spectralon(copyright), further described in an article entitled Handbook of Applied Photometry, Chapter 5, Measurement Procedures, AIP Press, pp. 133-177, and CIE 127-1997 Technical Report, Measurement of LEDs. As is well-known, such measurements involve measuring the spectral flux emitted by the lamps, from which are calculated the characteristics of total radiant flux (watts), total photopic flux (lumens), spectrum (peak wavelength, center wavelength, centroid, and full width half maxxe2x80x94FWHMxe2x80x94) and chromaticity (x,y, dominant wavelength and parity).
In more recent years, with the emergence of light emitting diodes, LEDs have become an important alternate light source with efficiencies greater than incandescent and fluorescent lamps and with further advantages of small size, light weight and durability. These applications, however, have placed stringent demands on the optical characteristics of LEDs, which serve as the baseline for product quality and product design.
The above-mentioned characteristics of small physical size and also flux levels, spectrum and spatial distribution, moreover, separate LEDs from typical light sources which are generally employed and measured for photometric and radiometric quantities. With LEDs, on the other hand, it is often difficult to achieve a high-level of photometric or radiometric measurement accuracy due to uncertainties within that type of measurement equipment and test set-up. Additionally, traditional photometrics, because of their inability to simulate the response of the human eye at the ends of the visible spectrum, can generate significantly flawed data when testing red, blue and white LEDs.
The obvious difference in size between light bulbs and LEDs, furthermore, presents additional difficulties as well, such as marking an identity number on each LED and obviating the awkwardness in repeatedly handling the fragile leads of LEDs, plugging them in and out, especially during life testing.
The present invention, accordingly, addresses all of the above problems, providing a novel cassette structure for holding multiple LEDs on a single cassette for both burn-in and then for integrated sphere optical measurements during life testing, while enabling a large enough space for identification marking and eliminating the need repeatedly to plug the LED leads in and out, and with the cassette containing contacts rated for multiple insertionsxe2x80x94the cassette being the only item that is inserted and removed. Underlying the invention is an operation whereby all of the cassette-mounted LEDs are lighted simultaneously during burn-in, and all of the cassette-mounted LEDs are mounted in the integrating sphere for measurement testing, but they are (sequentially or successively) lighted separately and individually, for such measurements.
n object of the present invention, therefore, is to provide a new and improved method of and cassette structure for high-speed multi-purpose LED testing, and that addresses the previously described prior testing and handling limitations.
A further object is to provide a novel LED test station for enabling burn-in and optical integrated sphere spectral flux measurements.
Other and further objects will be explained hereinafter and are more fully delineated in the appended claims.
In summary, however, from one of its important viewpoints, the invention embraces a method of holding multiple LEDs for burn-in and optical and electrical life testing measurements, that comprises, providing a cassette with contacts rated for multiple insertions and adapted to receive the plurality of LEDs with leads thereof plugged therein; inserting the cassette holding the plurality of LEDs into a fixture board and electrically energizing the LEDs within the cassette to light all the LEDs simultaneously for burn-in; thereupon inserting the cassette holding the plurality of LEDs within a light-integrating sphere system and successively lighting each LED individually while conducting optical and electrical life-testing measurements thereof within the sphere system.
Preferred and best mode designs and implementation are later presented.